The invention relates to obtaining fiber textures of carbon by carbonizing a cellulose precursor.
“Fiber textures” is used herein to designate various types of textures such as yarns, unidirectional sheets made of parallely extending filaments or yarns and bidimensional (2D) or tridimensional (3D) fiber sheets or clothes such as obtained by weaving, knitting or braiding.
Because of their low thermal conductivity, cellulose-precursor carbon fibers are used in particular for fabricating ablation materials, typically for internal wall linings for nozzles and/or for combustion chambers of rocket engines. The term “ablation material” is used to mean a material which, in operation, is progressively eroded by being exposed to a stream of gas at high temperature. Other applications for cellulose-precursor carbon fibers exist or could be envisaged.
Until recently, the cellulose precursor used did not enable carbon fibers to be obtained having remarkable mechanical properties. Typically, the carbon fibers obtained had breaking strength in traction of about 600 megapascals (MPa) and a Young's modulus of about 40 gigapascals (GPa). In addition, the cost of such carbon fibers was high, in particular about 10 to 15 times greater than the cost of high-strength carbon fibers obtained with a polyacrylonitrile precursor.
Processes described in US patent applications Nos. US 2002/0182138, US 2002/0182139, and U.S. Pat. No. 6,967,014, the contents of which are incorporated herein by way of reference, have enabled carbon fibers to be obtained from cellulose precursors of relatively low cost, of the kind commonly used in industry, such as the rayons used for reinforcing tires, and have also enabled the mechanical properties of cellulose-precursor carbon fibers to be improved. Typically, a breaking strength in traction of at least 1200 MPa and a Young's modulus of about 40 GPa or considerably more can be obtained.
Those known processes consist in impregnating the precursor fibers prior to carbonization with an organosilicon additive in solution in an organic solvent such as perchloroethylene. The cellulose precursor used is in the form of yarns or woven cloth in which the fibers are coated in oil that is put in place during fabrication of the yarn in order to facilitate the textile operations to which the yarn is subjected, in particular weaving. It is necessary, or at least preferable to eliminate the oil, or sizing, prior to impregnation with the organosilicon additive(s). That is done by washing using organic solvents such as solvents of the tetrachloroethylene type. The solvents used for removing the oil or for dissolving the organosilicon additives raise environmental problems and they are expensive to recycle.